Fast automatic gain control (AGC) for packet based systems

Abstract

A method and apparatus for use in a packet based wireless communication system for reducing automatic gain control (AGC) convergence time at a receiver are described. A radio frequency (RF) signal is received. The RF signal includes a sequence of a plurality of pre-defined power levels at a beginning of a preamble of the RF signal. Statistics for each of the plurality of pre-defined power levels at the beginning of the preamble of the RF signal are computed. An appropriate gain for a variable gain amplifier (VGA) is then computed based on the computed statistics for each of the plurality of pre-defined power levels and a-priori information related to transmission power differences between the plurality of pre-defined power levels of the sequence.

What is claimed is: 
     
       1. A method for use in a packet-based wireless communication system for reducing automatic gain control (AGC) convergence time at a receiver, the method comprising:
 receiving a radio frequency (RF) signal including a preamble portion and a data portion; 
 applying a pre-defined sequence of gain levels at a variable gain amplifier (VGA) to the preamble portion of the RF signal; 
 computing statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the RF signal; and 
 computing an appropriate gain for the VGA based on the computed statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the RF signal. 
 
     
     
       2. The method of  claim 1 , further comprising:
 updating a gain of the VGA based on the computed appropriate gain to receive the data portion of the RF signal. 
 
     
     
       3. The method of  claim 1 , wherein the packet based wireless communication system is an IEEE 802.11ad packet-based system. 
     
     
       4. The method of  claim 1 , further comprising:
 storing, in a buffer, the computed statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the received RF signal, until a start-of-packet (SoP) is detected. 
 
     
     
       5. The method of  claim 4 , wherein computing the appropriate gain for the VGA is performed when the SoP is detected. 
     
     
       6. The method of  claim 1 , further comprising:
 storing the computed appropriate gain for the VGA in a memory, wherein the stored computed appropriate gain is indexed by a corresponding link identifier. 
 
     
     
       7. The method of  claim 6 , further comprising:
 extracting a previously computed appropriate gain for the VGA from the memory based on the corresponding link identifier; and 
 updating a gain of the VGA based on the extracted previously computed appropriate gain. 
 
     
     
       8. A wireless transmit/receive unit (WTRU) configured to operate in a packet-based wireless communication system by reducing automatic gain control (AGC) convergence time at a receiver in the WTRU, the WTRU comprising:
 the receiver coupled to a baseband processor, a transmitter and an antenna; 
 the receiver configured to receive a radio frequency (RF) signal including a preamble portion and a data portion; 
 the receiver configured to apply a pre-defined sequence of gain levels at a variable gain amplifier (VGA) to the preamble portion of the RF signal; 
 the receiver configured to compute statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the RF signal; and 
 the receiver configured to compute an appropriate gain for the VGA based on the computed statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the RF signal. 
 
     
     
       9. The WTRU of  claim 8 , wherein:
 the receiver is configured to update a gain of the VGA based on the computed appropriate gain to receive the data portion of the RF signal. 
 
     
     
       10. The WTRU of  claim 8 , wherein the packet based wireless communication system is an IEEE 802.11ad packet-based system. 
     
     
       11. The WTRU of  claim 8 , wherein:
 the receiver is further configured to store, in a buffer, the computed statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the received RF signal, until a start-of-packet (SoP) is detected. 
 
     
     
       12. The WTRU of  claim 11 , wherein:
 the receiver is configured to compute the appropriate gain for the VGA is performed when the SoP is detected. 
 
     
     
       13. The WTRU of  claim 8 , wherein:
 the receiver is further configured to store the computed appropriate gain for the VGA in a memory, wherein the stored computed appropriate gain for the VGA is indexed by a corresponding link identifier. 
 
     
     
       14. The WTRU of  claim 13 , wherein:
 the receiver is configured to extract a previously computed appropriate gain for the VGA from the memory based on the corresponding link identifier; and 
 the receiver is configured to update a gain of the VGA based on the extracted previously computed appropriate gain. 
 
     
     
       15. A method for use in a packet-based wireless communication system for reducing automatic gain control (AGC) convergence time at a receiver, the method comprising:
 receiving a packet in a wireless radio frequency (RF) signal, wherein the packet includes a preamble portion and a data portion; 
 applying a pre-defined sequence of gain levels at a variable gain amplifier (VGA) to the preamble portion; 
 computing statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the RF signal, wherein the statistics correspond to one or more of a signal power, a signal amplitude, a signal root mean square (RMS) value, and a peak-to-peak signal amplitude; 
 computing an appropriate gain for the VGA based on the computed statistics when each of the pre-defined sequence of gain levels is applied to the preamble portion of the RF signal; and 
 amplifying, by the VGA, the data portion of the packet, based on the computed appropriate gain. 
 
     
     
       16. The method of  claim 15 , wherein the packet based wireless communication system is a cellular based wireless communication system. 
     
     
       17. The method of  claim 15 , wherein the packet is received from a base station.